1. Field of the Invention
The present invention relates to a method of separating a heavy metal ion by use of a chitosan, and in particular to a method of separating a heavy metal ion by use of a chitosan derived from a chitosan-producing microorganism.
2. Detailed Description of the Prior Art
A method of separating and removing a heavy metal ion from an aqueous solution containing the heavy metal ion by treating the aqueous solution with a chitosan, is known (Japanese Patent Publication (KOKOKU) No. 5834/1976). In the method is used a chitosan obtained by smashing the shell of a crustacean such as shrimps and crabs, treating the smashed shell with alkali to remove proteins, treating the resulting product with acid to remove calcium contents, thereby producing a chitin, and then hydrolyzing the chitin to carry out deacetylation. However, the chitosan used in this method has the problems that the process of preparation thereof is complicated as described above, and, in addition, that it has poor adsorptivity for heavy metal ions, which is presumably caused by its low molecular weight resulting from the harsh alkali treatment and acid treatment.
In order to improve the heavy metal ion adsorptivity of the crustacean-derived chitosan, there have been proposed a method in which the chitosan is reacted with a particular cationizing agent or anionizing agent (Japanese Pre-examination Patent Publication (KOKAI) No. 118,485/l986) and a method in which the chitosan with a low molecular weight is crosslinked with an organic diisocyanate compound (Japanese Pre-examination Patent Publication (KOKAI) No. 133,143/1986).
However, the methods described in the Japanese Pre-examination Patent Publication (KOKAI) Nos. 118,485/1986 and 133,143/1986 have the drawback that they do not eliminate the complication of said method using the shell of crustaceans, but make the preparation process more complicated.